Fuel injection system for internal combustion engines

ABSTRACT

In a fuel injection system, in order to prevent an intake air sensor to transmit those forces to a fuel control valve which are generated upon sudden thrusts of air in the engine intake tube, there is provided a valved passage which connects intake tube portions upstream and downstream of the intake air sensor and which opens in response to a predetermined pressure differential prevailing across the intake air sensor.

United States Patent I [191 Knapp et al. [4 1 Jan. 16, 1973 [54] FUEL INJECTION SYSTEM FOR [56] References Cited INTERNAL COMBUSTION ENGINES UNITED STATES PATENTS [75] Inventors: Heinrich Knapp, Leonberg-Silberberg; Reinhard Schwartz, Suntgeuvgglson ..26l/50A of Germany 1,955,204 4 1934 Sawyer 73 Assignee; RobertBosch Gmb", Stuttgart, 3,613,650 10/1971 Stumpp et al ..261/50 A 1 many Primary Examiner-Benjamin W. Wyche [22] Filed: 1971 Assistant Examiner-Randall Heald [21] Appl. No.2 107,631 Att0rney-Edwin E. Greigg [30] a Foreign Application Priority Data [57] ABSTRACT I In a fuel injection system, in order to prevent an in- "'7' 197-0 Germany "f 02 take air sensorto transmit those forces to afuel con- [52] U S Cl 123/119 R, 139A, 261/64 C trol valve which are generated upon sudden thrusts of [5 1] lmzm 7/00 air in the engine intake tube, there is provided a [58] Field 261/50 A valved passage which connects intake tube portions 261/64 R, 64 B, 64 C; 137/87, 88

upstream and downstream of the intake air sensor and which opens in response to a predetermined pressure differential prevailing across the intake air sensor.

MNNTEDJAX 16 I975 SHKU 1 [1F 3 PATENTED M 19 3.710.769

SHEEI 2 [IF 3 Fig.2

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION This invention relates to a fuel injection system for an externally ignited internal combustion engine wherein fuel is continuously injected in the inlet conduit, in which an air sensor and an arbitrarily controllable throttle valve are installed. The air sensor is disair by means of the pressure differentialbetween the air pressure upstream and downstream of the air sensor.

This displacement of the sensor is opposed by a preferably constant restoring force. The sensor, in proportion to its displacement, actuates a fuel metering valve. In this manner, a constant ratio between the amount of air and the amount of fuel introduced into the inlet conduit downstream of the air sensor can be maintained.

The purpose of fuel injection systems of the aforenoted type is to ensure that a favorable air fuel ratio is achieved automatically for a spark-ignited engine under all performance conditions. In this manner the fuel combustion is as complete as possible resulting in a superior engine efficiency and further, the formation of poisonous discharge gases is avoided or at least decreased to a permissible value to achieve this, the fuel amount must be metered very accurately for all possible performance conditions. It is necessary that the aforenoted proportionality between the air amount and the fuel amount be maintained substantially undisturbed, but be variable as a function of such engine parameters as load, r.p.m. and temperature (the so-called A-adjustment).

In a fuel injection system of the aforenoted type (as disclosed, for example, in US. Pat. No. 2,583,406), the restoring force exerted on the air sensor is generated by a spring, the bias of which is variable as a function of the engine temperature (an engine parameter).

In case the engine is running idle or the vehicle is coasting in gear and suddenly the throttle valve is turned to a position, which corresponds to a higher r.p.m. of revolution for normal operation, the air sensor of a conventional fuel injection system is subjected to an abrupt deflection from its previous position. The reason for this is that, in addition to the increased flow rate of air, the volume of the intake conduit has to be charged from a low pressure to a higher pressure. This results in a disadvantageous supersaturation of the air fuel mixture. Furthermore, the high initial momentum causes overswings of the air sensor, due to its inertia. Thus, the said supersaturation is aggravated.

OBJECT AND SUMMARY OF THE INVENTION placed, in proportion to the throughgoing flow rate of It is an object of the invention to provide an imsensor are connectable to one another by a valve which is opened, when its closing force is overcome. This occurs when the pressure differential across the air sensor exceeds the value required to move theair sensor. By virtue of said connecting valve, the unfavorabie'initial thrusts are either eliminated or substantially reduced.

parent from the ensuing detailed specification of several exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional, partially schematic view of a fuel injection system incorporating a first embodimentof the invention; I

FIG. 2 is a sectional view of a second embodiment of the invention;

FIG. 3 is a sectional view of a third embodiment of the invention; and

FIG. 4 is a sectional view of a fourth embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS Turning now to FIG. 1, the combustion air flows in the fuel injection system through a filter 1 in the direction indicated by the arrows and passes through an inlet conduit portion 3 in which an air sensing device 4 is installed. Thereafter, the air passes through a coupling hose 5 and through an inlet conduit portion 6, provided with an arbitrarily controllable throttle valve 7. The sensor 4 moves in the inlet conduit portion 3 as an approximately linear function of the How rate of air passing through the inlet conduit. The sensor '4 is formed as a plate arranged normal to the direction of the air flow. It is tiltable about a pin 9 against the force of a restoring spring 8. The pin 9 is fastened to a lever 10 to which movements of the sensor 4 are transmitted. Lever 10 is pivotally supported with low friction on a shaft 11 and, upon its displacement, actuates with its nose 12, a movable valve part 13 of a fuel metering and distributing valve 14. The restoring force is provided by a spring 15 which has a very flat performance characteristic, so that when the sensor 4 is displaced and, accordingly, the spring 15 is compressed, its return force remains approximately constant irrespective of the extent of compression. The position of rest of the lever 10 is adjustable by a set screw 16.

The fuel is supplied by a feed'pump 18, driven by an electric motor 19. The fuel is drawn by pump 18 from a tank 20 and forcedthrough a fuel line 21 to the fuel metering valve 14. A return conduit 22 is branched off from the fuel line 21 and contains a pressure limiting or.

pressure maintaining valve 23. The fuel which is metered by the metering valve 14, flows from ports 24 to individual injection valves, which generally are installed in the inlet conduit in the proximity of the corresponding engine cylinders.

Filter housing 1 and inlet conduit portion 3 are builtas a structural unit in such a manner that the intake air drawn by the engine, immediately upon passing I through filter 2, impinges on the surface of sensor plate 4 which maintains the inlet conduit closed when the engine is not running. Said surface may be considerably larger than the surface of throttle valve 7; the working capacity of sensor plate 4 will then be large. Since filter 2 should have a relatively large diameter in any case,

there is thus no difficulty in making thersensor plate 4 correspondingly large. The butterfly valve 7, on the other hand, can be relatively small to take up as little space as possible.

The spring 8 is so adjusted that as soon as the pressure differential across sensor 4 exceeds the pressure differential, that is sufficient to actuate the sensor 4 against the force of spring 15, the sensor plate 4 is tilted around pin 9 against the force of spring 8. An aforenoted excess of pressure difference occurs as a result of sudden pressure thrusts when upon depressing the accelerator ad upon corresponding opening of the butterfly valve during idling or coasting in gear the volume of the inlet conduit has to be charged from a low pressure to a high pressure by the air flowing at an increased rate.

FIG. 2 illustrates another embodiment of the invention. Here the sensor 4a is fixedly (i.e., nontiltably) fastened to lever 10. For diverting the overpressure, the inlet conduit portion 3 is provided with a bypass 25 which interconnects inlet conduit portions upstream and downstream of the sensor 4a and which is closed by a check valve 26 loaded with a spring 27. The force of the latter is so adjusted with respect to spring 15 that when the pressure differential across sensor 4a is larger than the pressure differential that is sufficient to actuate the sensor 4a against the force of spring 15, the check valve 26 is unseated by'theintake air pressure, overcoming the forcerof the spring 27. As a result, the bypass 25 is opened. The bias or preload of spring27 is variable by a temperature sensitive member 40. In this manner, for example, the bias or preload of the spring of the air fuel ratio is expedited. which is desirable for this engine' condition. In any event, however, the said overswing always remains sufficiently small so as not to cause adverse effects.

FIG. 3 illustrates a structurally particularly simple embodiment of the invention. Here again, as in the embodiment shown in FIG. 2, the sensor 4b is rigidly affixed to the lever 10. In this embodiment the overpressure valve means is formed of a check valve 30, which is biased by means of a spring 29 and which controls an orifice 28 in the sensor 4b. The force of spring 29 is so adjusted with respect to spring 15 that when the pressure differential upstream and downstream of sensor 4b is larger than'the pressure differential that is sufficient to actuate the sensor 4b against the force of spring 15, the check valve 30 is unseated by the intake air pressure, overcoming the force of the spring 29. As a result, the orifice 28 is'opened.

The embodiment of the invention illustrated in FIG. 4 includes a. sensor 40, movable linearly along the axis of the inlet conduit. For this purpose, sensor 40 is attached to one end of a guide rod 32 which is supported axially displaceably in a sleeve 33 which, in turn, is held fixedly in, and coaxially with the inlet conduit. To the other end of guide rod 32 there is threadedly attached a coupling element 34 provided with a circumferential annular groove 35. In the inlet conduit there :is rotatably held a shaft 36, the axis of which crosses over perpendicularly that of the inlet conduit. To shaft 36 there is affixed a lever 37carrying at its free end a follower pin 38 which extends into the groove 35. To lever e 37, at a location between shaft 36 and pin 38, there is hooked one end of a return spring 41, having the same function as springs 15 in the previously discussed embodiments. The movable valve component'of the fuel metering valve is actuated by means of the rotation of shaft 36. Such a rotation, in turn, is caused by the motion of guide rod 32. For providing a relief of overpressure, the sensor 40 rod 32 against the force of a return spring 39. Upon such an occurence, the annular gap defined by the periphery of sensor 40 and the inner wall of conduit portion 3 is increased without. affecting the position of shaft 36 and thus without adversely affecting the fuel metering valve. The force of spring 39 is so-adjusted with respect to spring 41 that as soon as the pressure differential across sensor 4c exceeds the pressure differential that is sufficient to actuate the sensor 4c against the force of spring 41, the sensor 40 slides on and with respect to guide rod 32, compressing the spring 39. I What is claimed is: v V 1. In a fuel injection system for an internal combustion engine having an inlet conduit for the intake of air, said system being of the known type that includes ferential formed of the difference between the pressures prevailing in said inlet conduit upstream and downstream of saidair sensor, (e) a fuel metering a valve, the position of which is dependent upon the extentof displacement of said air sensor and (d) means operatively connecting said air sensor to said fuel me tering valve, the improvement comprising A. passage means interconnecting a location in, said inlet conduit upstream of said air sensor with a losensor,

B. valve means disposed insaidipassage means to control the flow passage section thereof and C. bias means for urging said valve means into 'a closed position obstructing said passage means; the force of said bias means being so designed that said valve means being openable against said bias means by said pressure difference whenreaching'a predetermined value over the value necessary to displace said air sensoragainst the force of said constant resetting means. i

2; An improvement as defined in claim .1, including means to vary the'forc'e of said bias means as a function of temperature...

3. An improvement as defined in claim 1, including A. a plate constituting said airsensor and said valve means,

B. a lever forming part of said means operatively connecting said air sensor to said fuel metering valve,

C. a pivot pin eccentrically and swingably securing said plate to said lever and is displaceableaxially on and with respect to the guide cation in said inlet conduit downstream'of said air D. a spring, constituting said bias means, engaging said lever and said plate to urge said plate into said closed position. 1 i

4. An improvement as defined in claim 1, including A. a bypass extending externally of said air sensor and constituting said passage means,

B. a check valve controlling said bypass and constituting said valve means, and

C. a spring, constituting said bias means, urging said check valve into said closed position.

5. An improvement as defined in claim 1, including A. an orifice provided in said air sensor and constituting said passage means,

B. a check valve mounted on said air sensor for controlling said orifice, said check valve constitutes said valve means and C. a spring supported on said air sensor for urging said check valve into said closed position, said spring constitutes said bias means. 6. An improvement'as defined in claim 1, including A. a plate constituting said air sensor and said valve means,

' B. a guide rod displaceable axially in said inlet con- 

1. In a fuel injection system for an internal combustion engine having an inlet conduit for the intake of air, said system being of the known type that includes (a) an arbitrarily operable throttle valve disposed in said inlet conduit to vary the flow rate of intake air, (b) an air sensor disposed in said inlet conduit and displaceable against the force of a constant resetting means to an extent proportional to the flow rate of intake air, said air sensor is displaceable by a pressure differential formed of the difference between the pressures prevailing in said inlet conduit upstream and downstream of said air sensor, (c) a fuel metering valve, the position of which is dependent upon the extent of displacement of said air sensor and (d) means operatively connecting said air sensor to said fuel metering valve, the improvement comprising A. passage means interconnecting a location in said inlet conduit upstream of said air sensor with a location in said inlet conduit downstream of said air sensor, B. valve means disposed in said passage means to control the flow passage section thereof and C. bias means for urging said valve means into a closed position obstructing said passage means; the force of said bias means being so designed that said valve means being openable against said bias means by said pressure difference when reaching a predetermined value over the value necessary to displace said air sensor against the force of said constant resetting means.
 2. An improvement as defined in claim 1, including means to vary the force of said bias means as a function of temperature.
 3. An improvement as defined in claim 1, including A. a plate constituting said air sensor and said valve means, B. a lever forming part of said means operatively connecting said air sensor to said fuel metering valve, C. a pivot pin eccentrically and swingably securing said plate to said lever and D. a spring, constituting said bias means, engaging said lever and said plate to urge said plate into said closed position.
 4. An improvement as defined in claim 1, including A. a bypass extending externally of said air sensor and constituting said passage means, B. a check valve controlling said bypass and constituting said valve means, and C. a spring, constituting said bias means, urging said check valve into said closed position.
 5. An improvement as defined in claim 1, including A. an orifice provided in said air sensor and constituting said passage means, B. a check valve mounted on said air sensor for controlling said orifice, said check valve constitutes said valve means and C. a spring supported on said air sensor for urging said check valve into said closed position, said spring constitutes said bias means.
 6. An improvement as defined in claim 1, including A. a plate constituting said air sensor and said valve means, B. a guide rod displaceable axially in said inlet conduit parallel to the direction of air flow therein, said guide rod forms part of said means operatively connecting said air sensor to said fuel metering valve, C. means for axially slidably securing said plate on said guide rod and D. a spring supported on said guide rod for urging said plate into said closed position, said spring constitutes said bias means. 